You may not have heard of Robert Ethan Saylor, but his death in January should inspire something more lasting than a small-town police investigation.

Saylor, who was known as Ethan, had Down syndrome, a genetic condition that causes learning difficulties. He was 26 and lived with his family in New Market, Md., in Frederick County. On the day he died, he went to a local mall to see the film “Zero Dark Thirty.” When it ended, his caregiver went to get the car. Saylor went back in and sat down for the next showing.

Theater employees told him to buy another ticket or leave. When Saylor refused, they called mall security, three off-duty county sheriff’s deputies who tried to drag him out of the theater. According to the Sheriff’s Office, Saylor cursed and struggled. He was handcuffed and ended up on the floor. Something happened, and then he died.

The medical examiner said it was a homicide, by asphyxiation. The county state’s attorney is considering whether to take the case to a grand jury.

Joe Espo, a lawyer who is representing the Saylor family, said the deputies “clearly had no idea of what they were getting into or how to de-escalate the situation or exercise the judgment to say this just wasn’t worth it.” Espo said witnesses heard Saylor cry, “I want my mommy!”

He described Saylor as a friendly guy known for giving long hugs and as a police buff. “He was just sort of entranced by law enforcement,” Espo said. “He liked speaking to them and visiting them and until that day had OK interactions with them.”

All parents worry about their children, but those whose children have developmental disabilities have a particular burden. They worry about acceptance, about shielding their children from cruelty and ignorance.

And they worry about physical harm. On the blog of a group called Down Syndrome Uprising, parents are talking about Ethan Saylor and are angry about the misinformation, stereotypes and even violence toward people with mental disabilities. “This violence is a symptom of how we view people who are different from us,” one mother wrote.

Her post reflects the impatience of parents at odds with a society unwilling to accept their children’s full humanity. The abuse of the disabled is a symptom. So is the recurring tragedy of police agencies unable to deal with people who are not criminal or dangerous, but vulnerable. We don’t know how this confrontation turned lethal — whether it was excessive force, lack of training or some unavoidable accident — though it is disturbing that Frederick County does not teach officers how to handle encounters with the mentally disabled.

Without prejudging the Saylor investigation, it is easy to see the truth in that mother’s observation. In a society that values equality, intellectual differences remain a barrier to acceptance. People with mental disabilities see it all: dismissal, contempt, affectionate pity. People look into the rounded face and unguarded gaze of someone with extra chromosomes and see a stereotype: a child who is lovable, adorable, maybe a little stubborn. What they do not see is an individual — or an equal.

Thursday is World Down Syndrome Day. Its goal is “to raise people’s awareness and understanding of Down syndrome.” It is well meaning, but for some that is not enough anymore. As Down Syndrome Uprising puts it: “Done with awareness. Moving on to acceptance.”